[Strawbale] reflectivity

[Jeff Ruppert]

Water glass is a solution that contains silica which bonds to calcium 
carbonate to form a vapor permeable barrier that sheds moisture.  It is 
the same concept as mixing lime, or cement, and adding sand (silica).  
Lime bonds and etches silica, which creates the fundamental bond within 
concrete, mortar, plaster, etc.  By adding a thin layer of silica over 
the lime, or cement, plaster in the form of a spray, you create the same 
bond between molecules on the surface of the plaster. 

Another way to think of it is as a pozzolan.  You are adding a type of 
silica to the lime that is readily available to bond with.  Some types 
of silica bond better than others, as is the case with clay (poor bond) 
as opposed to volcanic ash, or rice hull ash, or fly ash (good bond).

In this case you are creating a thin shell of silica and calcium that 
will, over time, break down due to it's relative "thin-ness" and you 
will need to do it again in a few years.  As stated above, it is vapor 
permeable.  One form of this is siloxane, which is a more industrial 
form and can be expensive.  They are all solutions that hold silica in 
suspension, keeping it ready for the reaction with calcium carbonate.

Jeff